The Downside of Northern Exposure
Point Barrow, Alaska, may not seem like a place where you should worry about too much exposure to the sun. But fair-skinned residents of this northernmost U.S. town may have to think seriously about wearing sunscreen this summer. The tattered ozone layer lets up to 70% more harmful ultraviolet rays reach the ground there now than it did 7 years ago, according to a report in the latest Geophysical Research Letters.
Increased exposure to ultraviolet B (UV-B), in particular, worries scientists, because these rays are for unknown reasons more damaging than others to skin and eye tissue. In the late 1980s, satellites began to track an increase in UV radiation passing through an ozone layer thinned by synthetic chlorofluorocarbons. But the only way to know how much reaches the ground is to measure it there, says Kevin Gurney, an atmospheric scientist at the University of California, Santa Barbara.
Gurney set up shop at Point Barrow, where he used a high-resolution spectroradiometer to measure the intensity of light at various wavelengths. From 1991 to 1996, Gurney measured UV-B at 18 wavelengths between 290 and 340 nanometers (nm). He found the sharpest increase over that period at 305 nm; the amount of rays at this wavelength that reached the ground every month rose 3% to 10% over the corresponding month in the previous year, except in June, which, curiously, showed a decrease in average radiation levels. The findings support previous work showing that ozone tends to absorb more UV radiation at 300 nm and almost none at 340 nm.
Although ground-level studies have pointed to increased UV-B levels in Argentina, Canada, and Greece, Gurney's findings from the northernmost latitude studied so far could have troubling consequences for people and animals exposed to the rays. That's because organisms at such high latitudes get a double whammy: direct exposure to UV-B and exposure to rays reflected from the nearly perennial snow cover. "I would like to see if the data are robust enough to look for trends in cataract incidences," says Gurney.